With near exponential growth in the use of microelectronics in virtually all sectors of our economy and in our personal lives, demand for integrated circuits and semiconductor devices has grown quickly. In order to keep up, manufacturers have striven to continuously boost their manufacturing capacity to meet the ever-increasing demand for goods that incorporate microelectronic devices.
In order to increase their yield, i.e. the percentage of useable microelectronic devices output by their fabrication facilities, and to further increase the quality of their goods, manufacturers have increasingly turned to automated inspection processes and methods to assist them in identifying defective microelectronic devices and in determining the root causes of the identified defects. Using these automated inspection methods has effectively increased production capacity by allowing manufacturers to ensure that a larger percentage of the products produced is useable. The higher quality of the resulting goods also helps the manufacturers by assisting them in maintaining and/or increasing their revenue by making their products more desirable.
In addition to inspecting the microelectronic devices themselves, there is a growing trend toward inspecting the back side and edges of the silicon wafers on which microelectronic devices are fabricated. Inspection of the backside of the wafers on which the microelectronic devices are fabricated can identify defects in the wafer itself or in the microelectronic devices on the obverse side of the wafer. Identifying defects on the backside of a wafer allows a manufacture to catch problems earlier in the fabrication process and can help pinpoint problems in the fabrication process itself that may be solved so as to increase the yield for future device manufacturing.
One problem with current backside inspection systems emanates from the fact that the front side of a wafer has delicate structures formed thereon that do not allow for superfluous manipulation of the wafer. It is entirely too easy to damage or destroy a valuable wafer and the microelectronic devices formed thereon. This danger is further complicated by the fact that the only locations on a wafer that may be positively grasped by a manipulator are the edges of the wafer. Generally, manufacturers allow for an edge exclusion zone around the periphery of the wafer that is between 3 and 10 mm in width, though these dimensions often vary between manufacturers and applications.
One existing system used in the wafer inspection industry is described in U.S. Pat. No. 6,204,917. This device includes a set of grooved wheels to rotate the wafer on an air bearing surface while a camera is inspecting the front side and back side at the same time. One problem with this design is that edge rolling of the wafer to spin it can create particles that will contaminate the surfaces of the wafer. Another problem with this design is that it is difficult to accurately predict the rotation angle of the wafer because the rolling contact with the edge could slip.
Other systems utilize known imaging methods in conjunction with a three-axis robotic device or manipulator that rotates the wafer about three orthogonal axes generally referred to as X, Y and Z. An example of one such system is the INS 3300 marketed by Leica Microsystems of Wetzlar, Germany. This system uses a robot to manipulate the wafer during inspection. Because wafers do flex somewhat as a result of such manipulation, it is possible to damage the wafer itself and/or the microelectronic structures formed thereon, and such manipulations are therefore disfavored by many manufacturers.
Accordingly, there is a need for a wafer handling system that minimizes stress placed on a wafer, while allowing clear access to the backside of the wafer for inspection.